The trial halted this week by the National Institutes of Health is but the latest failure in the realm of would-be HIV vaccines. The study, known as HVTN 505, was testing a two-vaccine “prime-boost” strategy; the first vaccine was designed to prime the immune system, the second was intended to boost the immune response, explained the National Institute of Allergy and Infectious Diseases (NIAID).

In this case, the strategy didn’t appear to work. And on Thursday, the government called off the trial, effective immediately. Not only did the vaccine not prevent HIV infection, it didn’t even reduce viral load among those recipients who became infected with HIV.{C}

Given those circumstances, there appeared to be little point in continuing, the NIAID said in a statement.

“It is a remarkable disappointment that none of the vaccine approaches have worked to date,” said John Zaia, M.D., the Aaron D. And Edith Miller Chair in Gene Therapy at City of Hope. “From a scientific standpoint, it remains a challenge to determine how to activate the immune system to kill HIV when the virus thrives on activated immune cells.”

Further, during this trial, researchers found a “non-statistically significant” increase in HIV infection among those participants who received the vaccine, compared to the placebo group. Statistically relevant or not, those findings bear investigation, concluded an independent data and safety monitoring board.

Said the NIAID in a statement: "Based on the finding, the [board] recommended closer follow-up of participants beyond their month 24 study visit. NIAID concurred, and will, in concert with the study investigators, be amending the study protocol to allow for closer, extended follow up of the vaccine recipients."

The study had already enrolled 2,504 people in 19 cities, focusing on HIV-negative men and transgender people who have sex with men.

But all is not lost. Researchers around the globe are still trying to find a way to stop the disease. At City of Hope, scientists are exploring a “completely different” approach using gene therapy.

On Thursday, Zaia put that work – and the reaction to the latest vaccine failure – in context. “Our approach is a cellular strategy,” he said. “But we are nowhere near the phase II level of evaluation which was done here using thousands of patients.”

As the NIAID says on its website: "Historically, vaccines have been our best weapon against the world’s deadliest infectious diseases, including smallpox, polio, measles, and yellow fever. Unfortunately, we do not have a vaccine for HIV. HIV has unique ways of evading the immune system and the human body seems incapable of mounting an effective immune response against [the] virus. As a result, scientists do not have a clear picture of what is needed to provide protection against the virus."

Meanwhile, the Associated Press pointed out that, despite multiple AIDS vaccine failures over the years, a 2009 study in Thailand did show some success. It too used a prime-boost approach. "Newer research suggests another approach – to try creating powerful antibodies that could work a step earlier than the T-cell attack, before HIV gets inside the first cell," the AP said.

Zaia likely spoke for all researchers in summing up the week's developments: “Events like this make us want to move faster.”